This invention relates generally to removing oil from oily aqueous systems, and specifically to methods for removing tramp oil from aqueous solutions used as coolants in machining centers and those used as cleaning fluids to wash metal parts, such as hot jet spray washers.
If tramp oil is allowed to accumulate in a coolant or washer system it will cause operating problems, such as machine down time, increased tool wear and cleaning and filtering problems. Preventive maintenance and good housekeeping practices help reduce tramp oils, but they are never completely eliminated. Tramp oils in a coolant or washer system must be economically removed to extend fluid life and reduce or eliminate the problems caused by tramp oil contamination.
Coolants used in computer numerically controlled (CNC) machining centers and in hot jetspray washers commonly have problems associated with tramp oil collecting in the coolant solution. The major problem is that after a limited number of hours of use, the coolant solution must be discarded as hazardous waste because the tramp oil cannot be removed efficiently. In the early 1980's many CNC machines were converted to synthetic coolants. These coolants are located on the CNC machines in compact coolant tanks located below a work table in the machine, which makes it impossible to mount conventional oil skimmers without major modifications. Tramp oil reduces the cutting and cooling qualities of a coolant to the point that it must be drained and handled as a hazardous waste, which is very expensive to CNC operating companies. As a consequence, most CNC machine users return to the cheaper soluble oil coolant that requires frequent draining due to the tramp oil problem.
Hot jetspray washers clean motors, transmissions, and other dirty parts in a wide range of industries. They use aqueous cleaning solutions at high temperatures to scrub the contaminated material from the parts. As with CNC machines, a solution tank is located under the cleaning chamber where oil and grease emulsify with solution until it doesn't clean and must be disposed of as hazardous waste. Tank location and the violent water surface inside the storage tank prohibit conventional oil skimmers from being used.
Conventional oil skimmers fall into four categories. Disk skimmers require relatively calm surfaces, and constant liquid level to work well. When installed on a hot jetspray washer, these skimmers produce less than desirable results. Operators find it difficult to maintain liquid level high enough for the disk to reach tramp oil yet not have a problem with foam pouring out when the washer is in use. The typical disk type skimmer is found in U.S. Pat. No. 4,642,185, issued to Turner, et al. Another type of skimmer is a belt skimmer, typified by those disclosed in U.S. Pat. No. 4,642,372, issued to Threadgill, and U.S. Pat. No. 4,614,582, issued to Campitelli, distributed by Master Chemical Corporation, Perrysburg, Ohio. The smallest of these belt type skimmers is over three feet tall and is unacceptable for the high temperatures of hot jetspray washers. Liquid height in hot jetspray washers is 12 to 18 inches and 6 to 8 inches in CNC machines.
Further types of oil skimmers include floating tube or mop-rope type skimmers. These types of skimmers work well in large coolant systems, ponds, lakes, rivers or oceans but their size prohibits use in hot jetspray washers and CNC machines. A floating tube type skimmer is distributed by Oil Skimmers, Inc., Cleveland, Ohio. An oil mop type skimmer is disclosed in U.S. Pat. No. 3,748,682, issued to Rhodes, and distributed by Oil Mop, Inc., Belle Chasse, La.
A still further type of oil skimmer is the weir type skimmer which may be further broken down into stationary weir and floating suction weir concepts. The stationary weir concept works well with constant liquid height. However, the violent action inside a hot jetspray washer causes as much cleaning solution to be removed as oil. Also, the low height of CNC coolant tanks eliminates their use since they depend on gravity to drain off oils. The floating suction weir type on the other hand works well in calm systems removing up to 99% of the oil, but also removes far too much water in the violent action of a hot jetspray washer. The removed oil must be further processed to reduce water content. The floating suction weir type of oil skimmer is disclosed in U.S. Pat. No. 3,970,556 issued to Gore, and distributed by Douglas Engineering, Concord, Calif., and a similar type unit is distributed by Megator, Pittsburgh, Penna. The major problem with the floating type weirs is that they are larger than the liquid tank on most CNC or hot jetspray washer machines.
Prior to the subject matter of the present invention, the inventor herein tried to perfect a filtration and oil skimming unit for hot jetspray washers. The design used both belt and disk skimmers in a sidemount tank to replace the original disk skimmers. Through trial and error, the proper type of motor, disk and belt material were found for use in the 180.degree. to 240.degree. F. temperature range. However, while sidemount skimmers removed the oil, they had problems of heat loss and foam running out of the tank.
CNC machines and hot jetspray washers have one thing in common, a drain plug. It would be advantageous if this drain plug could be utilized to extend the production life of oil based, semi-synthetic and synthetic coolants and alkaline wash waters by removing free floating, disbursed and loosely emulsified tramp oils from the coolant reservoir or central system. It would further be advantageous to provide a tramp oil removal system that could operate not through the drain plug but over the side of the tank. It would also be advantageous if the oil removal system would work with other types of oils such as removing crude oil from oceans caused as a result of large oil spills in conjunction with other oil removing apparatus such as oil booms.